Oxycalciomicrolite
Chemical formula: Ca₂Ta⁵⁺₂O₇
Oxycalciomicrolite is a rare oxide from the microlite group, distinguished by its brownish-yellow to brownish-red color and occurrence in pegmatites.
Properties
- Mohs hardness
- 5-5.5
- Luster
- Vitreous to resinous
- Streak
- White
- Density
- 6.333
- Transparency
- Translucent
- Crystal system
- Isometric
Diagnostic features
## Identification Oxycalciomicrolite is identified by its characteristic octahedral crystal form, brownish-yellow to brownish-red color, vitreous or resinous luster, and high density. Its occurrence in granitic pegmatites is also an important indicator. ## Distinguishing from Similar Minerals It can be confused with other minerals from the microlite group (e.g., pyrochlore, microlite). Definitive differentiation requires advanced analytical methods, such as chemical composition analysis (EDS/WDS), due to very similar physical properties within the group. ## Crystal Forms It most often forms regular, octahedral crystals, which can reach several millimeters in size. Crystals occur as single individuals or in small clusters, overgrown on other minerals of the host rock.
Geological environment
## Genesis It is a mineral of magmatic origin, crystallizing in the late stages of the evolution of granitic pegmatites, rich in rare earth elements and tantalum. ## Mineral Associations It co-occurs with minerals typical of pegmatites, such as quartz, albite, microcline, muscovite, as well as with other tantalum and niobium minerals. ## Localities The most important and typical occurrence is the Fumal pegmatite in Nazareno, Minas Gerais, Brazil. This is the main locality from which the best-formed specimens of this mineral originate.
Rarity
Very rare
For collectors
## Quality Criteria The most prized oxycalciomicrolite specimens are those with sharp, well-formed crystals of regular, octahedral shape. An intense brownish-red color and good luster are desirable. Specimens where crystals are aesthetically set on a contrasting matrix, such as white albite or quartz, are also highly valued. ## Popular Localities The only known and significant collecting locality is its type locality – the Fumal pegmatite in Brazil. Specimens from this location are the standard for the species.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water may be used, but strong rubbing should be avoided. Always dry the specimen thoroughly after cleaning. ## What to Avoid Avoid contact with acids and strong chemical agents, which can damage the mineral's surface. Do not heat it or subject it to sudden temperature changes. As a brittle mineral, it is susceptible to mechanical damage. ## Storage It is recommended to store specimens in separate, padded boxes to prevent scratching by harder minerals. Protect it from impacts and falls. Display should be in stable conditions, away from direct sunlight and sources of vibration.